Active electronically scanned arrays (AESA) are now commonly used in multi-channel military radar systems to allow fast scanning of an area with beams of various frequencies. In AESAs, rather than mechanically steering an array aperture (e.g., by way of a gimbal), beam steering is accomplished electronically through manipulation of time and/or phase differences between signals radiated by the elements of the array. The performance of an AESA is therefore dependent on the precise establishment of relative time/phase relationships between signals emitted by the various elements of the AESA.
Antenna elements of AESAs are generally located in close proximity to one another (e.g., less than half of the operational wavelength between adjacent elements) for reasons related to array-dependent scan performance (such as grating lobes) requirements, or size, weight, and power (SWAP) platform constraints. As a result of this proximity, mutual coupling between elements of an AESA can distort the radiated output and received input from the elements. The distortion caused by mutual coupling can affect the relative magnitude and phase differences between signals at each of the antenna elements, which degrades performance of the AESA especially over ultra-wide bandwidths.
Conventional techniques for reducing the negative performance effects of mutual coupling of array elements generally seek to reduce the mutual coupling through modification of the antenna array hardware such as element shielding, array geometries, etc. However, these approaches can substantially increase the cost of an AESA, and may be incompatible with SWAP constraints of a platform to which the AESA is to be mounted. Conventional approaches based on signal processing techniques generally require simultaneous measurements of currents and/or voltages in each element of every pair of elements in an array in order to characterize the mutual coupling between all elements. These measurements may be time-consuming to collect, and may require costly specialized measurement hardware such as multi-port network analyzers.